In the old design, I was using the Planets theme. When it switched to the new design, it still had the Planets theme. But then I decided to see what some of the other themes looked like.

But apparently they don't let you choose the Planets theme anymore (even though it worked when I first switched?). Is there any way to get it back?

I've already tried reverting to the old design, changing the theme and then changing it back to planets, and then switching back to the new design. It kept what I had previously saved last time in the new design.